Functional traits associated with nitrogen use efficiency in wheat

Figures & data

Table 1. Definitions of NUE components according to Weih et al. (2011, 2014).

Symbol	Component	Calculation	Units
NUE	Nitrogen use efficiency	UN × EN,g × CN,g = Ng/Ns	g g^−1
UN	Mean N uptake efficiency during major growth period per N content in seed grain	N′/Ns	g g^−1
EN,g	Grain-specific N efficiency	Bg/N′	g g^−1
CN,g	Grain N concentration at final harvest	Ng/Bg	g g^−1
Ns	N content of seed (sown) grain		g
Ng	N content of produced grain at final harvest		g
N′	Mean plant N content during major growth period	Mean plant N content of two time points: the beginning and the end of the major growth period.	g
Bg	Biomass of produced grain at final harvest		g
B	Plant biomass at final harvest		g

Table 2. Varieties of wheat used in the climate chamber experiment.

NordGen accession no.	Name
n/a	Landrace Öland^a
n/a	Landrace Dala^a
n/a	Landrace Halland^a
NGB11010	Heines Kolben
NGB11280	Marquis
NGB13346	Sopu
NGB13441	Vastergotland
NGB13917	Vinjett
NGB6409	Halland
NGB6410	Dalarna
NGB6673	Landrace from Dalecarlia
NGB6675	Vårpärl
NGB6676	Kolben
NGB6677	Extra Kolben
NGB6678	Rubin
NGB6679	Diamant
NGB6680	Fylgia I
NGB6682	Progress
NGB6683	Ella
NGB6684	Rival
NGB6685	Fylgia II
NGB6686	Drott
NGB6687	Safir
NGB6688	Prins
NGB6689	Amy
NGB7455	Atle
NGB7456	Brons
NGB7457	Kärn
NGB7461	Svenno
NGB7462	Ring
NGB7464	Pompe
NGB7465	Snabbe
NGB7475	Kadett
NGB7479	Tjalve
NGB8923	Extra Kolben II
NGB9690	Aurore
NGB9691	Blanka
NGB9708	Dala
NGB9954	Dragon
NGB9955	Dacke
NGB9956	Sport

^aLandrace provided by local farmer.

Table 3. Monthly climate data for the duration of the field experiment, measured at Ultuna meteorological station about 8 km from the experimental site.

Month	Oct	Nov	Dec	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	∑
Mean temperature (°C)	4.5	5.1	−3.4	−9.0	−6.8	−1.6	5.3	11.0	15.0	20.4	16.5
Precipitation (mm)	55.2	59.8	28.1	26.5	26.1	41.7	29.1	54.1	38.0	68.5	89.0	516.1 (249.6^a)

^aTotal precipitation for spring wheat.

Figure 1. Plot of traits found to be important for nitrogen use efficiency (NUE) in the climate chamber experiment with 41 varieties of spring wheat, based on partial least squares (PLS) analysis. Circles represent the mean of four replicates. These important traits are (a) SPAD of the uppermost leaf at stem elongation (NUE = −307.0 + 12.9 × SPAD, R²= .40, p < .0001); (b) number of grains per ear (NUE = 112.1 + 4.8 × grains, R²= .16, p = .01); (c) number of ears per pot (NUE = 2.4 + 28.7 × ears, R²= .55, p < .0001); (d) straw biomass (B_st) (NUE = 86.2 + 7.6 × B_st, R²= .43, p < .0001); (e) days from emergence to anthesis (NUE = 705.0–5.7 × days, R²= .09, p = .052) and (f) days from emergence to senescence of the flag leaf (NUE = 635.5–2.9 × days, R²= .07, p = .10).

Note: Statistics for the PLS for each trait are presented in Table 4.

Table 4. Statistics derived from a partial least squares (PLS) analysis with NUE as the dependent variable, with one extracted factor.

	Parameter estimates for centred and scaled data	Model effect loadings	Model effect weights
Intercept	0.000
No. grains ear^−1	0.174	0.274	0.305
No. of ears pot^−1	0.324	0.524	0.570
Straw biomass	0.288	0.539	0.506
SPAD of top leaf at stem elongation	0.277	0.477	0.488
Days between emergence and anthesis	−0.134	−0.265	−0.235
Days between emergence and senescence	−0.113	−0.250	−0.199

Note: Observations are means of 41 varieties of spring wheat grown in four replications in a climate chamber.

Table 5. Results from ANOVA of several variables collected in a field experiment, showing F and p-values for the fixed effects.

Trait variable	Type		Fertilisation		Type*variety		Type* fertilisation		Type* fertilisation* variety		Spring wheat variety		Winter wheat variety		Spring wheat fertilisation* variety		Winter wheat fertilisation* variety
	F	p	F	p	F	p	F	p	F	p	F	p	F	p	F	p	F	p
NUE	191.9	<.0001	147.2	<.0001	22.2	<.0001	1.5	.26	1.5	.16	20.7	<.0001	23.7	<.0001	0.9	.50	2.2	.07
UN	66.6	.0002	174.1	<.0001	7.9	<.0001	0.5	.46	2.4	.02	12.8	<.0001	3.1	.02	1.4	.24	3.5	.008
EN,g	5.7	.06	25.6	.003	6.8	<.0001	0.4	.53	2.7	.01	10.2	<.0001	3.5	.008	2.2	.07	3.2	.01
CN,g	36.2	.009	105.0	<.0001	32.9	<.0001	0.2	.69	3.1	.003	36.6	<.0001	29.2	<.0001	2.0	.10	4.2	.002
Bg	38.9	.008	93.4	<.0001	12.2	<.0001	2.2	.19	1.9	.06	9.1	<.0001	15.2	<.0001	1.3	.30	2.6	.04
Ng	5.4	.10	99.4	<.0001	3.9	.0004	0.8	.40	1.7	.11	3.9	.004	4.0	.004	0.9	.50	2.4	.04
N′	16.2	.007	172.4	<.0001	1.3	.24	0.1	.77	2.5	.01	1.9	.11	0.8	.59	1.1	.36	3.8	.004
Ears m^−2	72.4	.003	40.0	<.0001	7.5	<.0001	0.8	.37	1.5	.15	4.5	.001	10.5	<.0001	0.8	.55	2.2	.06
Grains ear^−1	97.9	<.0001	73.5	<.0001	3.6	.0008	4.7	.06	2.0	.04	4.0	.003	3.2	.01	0.7	.64	3.4	.009
No. harvested grains	3.1	.18	101.8	<.0001	14.7	<.0001	1.0	.35	2.1	.04	6.1	.0001	23.4	<.0001	1.0	.43	3.3	.01
Straw biomass	9.3	.06	27.2	.002	1.2	.31	0.2	.70	0.7	.74	0.4	.84	2.0	.09	0.4	.82	0.9	.48
SPAD of flag leaf at anthesis	7.1	.02	137.4	<.0001	11.4	<.0001	0.1	.78	1.9	.07	12.6	<.0001	10.2	<.0001	0.2	.97	3.5	.007
Leaf biomass at end of major growth period	9.6	.02	39.5	.0008	1.5	.16	0.0	.86	2.6	.01	1.9	.10	1.1	.38	1.4	.23	3.7	.005
Translocation	5.7	.05	1.0	.36	4.1	.0003	0.7	.44	1.3	.28	5.9	.0002	2.3	.06	1.1	.36	1.4	.25
Yellow flag leaf area	48.2	.0004	18.7	.005	34.3	<.0001	13.9	.010	1.7	.11	39.0	<.0001	29.6	<.0001	1.0	.44	2.4	.05
Development	856.8	<.0001	0.5	.48	16.3	<.0001	1.5	.25	0.8	.62	18.6	<.0001	14.0	<.0001	1.1	.39	0.6	.73

Note: p-values < .05 in bold style.

Table 6. Pearson correlations between NUE or U_N and aboveground biomass of seedlings of six winter wheat varieties in a field experiment.

	Low N		High N
	Correlation coefficient	p	Correlation coefficient	p
UN vs. aboveground biomass in winter	−.74	.09	−.37	.47
NUE vs. aboveground biomass in winter	−.87	.02	−.50	.31
UN vs. aboveground biomass in spring	−.77	.08	−.45	.37
NUE vs. aboveground biomass in spring	−.91	.01	−.55	.25

Note: p-values < .05 in bold style.

Figure 2. Plot of SPAD against grain biomass (B_g) in a field experiment with spring and winter wheat varieties and two N treatments. SPAD refers to measurements taken on 2 July (winter varieties) and 9 July (spring varieties), that is, just after the major growth period, on 30 flag leaves per plot. Circles represent spring wheat and triangles winter wheat, open symbols represent the LN treatment and filled symbols the HN treatment. The equation for the relationship between the variables is B_g = −340 + 19xSPAD, and R²= .65.

Note: Statistics on correlations within and across treatments are presented in Table 7.

Figure 3. (a) Plot of total grain N (N_g) against mean N during the major growth period (N′) (N_g= 3.44 + 0.51×N′, R²= .64), (b) N_g against SPAD (N_g= −6.99 + 0.36×SPAD, R²= .86) and (c) N′ against SPAD (N′ = −11.03 + 0.46×SPAD, R²= .55), in a field experiment with spring and winter wheat varieties and two N treatments.

Notes: SPAD refers to measurements taken on 2 July (winter varieties) and 9 July (spring varieties), that is, just after the major growth period, on 30 flag leaves per plot. Symbols as in Figure 2. Insets show mean values for each group. Statistics on correlations between variables are presented in Table 7.

Table 7. Correlations (Pearson and Spearman) between NUE components and functional traits collected in a field experiment with spring and winter wheat at two fertiliser levels.

	Winter wheat				Spring wheat				Across (N = 4)
	Low N (N = 6)		High N (N = 6)		Low N (N = 6)		High N (N = 6)
	Correlation coefficient	p	Correlation coefficient	p	Correlation coefficient	p	Correlation coefficient	p	Correlation coefficient	p
NUE vs. SPAD at anthesis	.90	.02	.70	.12	.808	.05	.800	.06	.788	.21
Ng vs. SPAD	.94	.005	.82	.05	.312	.55	.459	.36	.998	.002
N′ vs. SPAD	−.06	.91	.51	.30	.586	.22	−.510	.30	.884	.12
N′ vs. Ng	.20	.70	.58	.23	−.163	.76	−.441	.38	.899	.10
EN,g vs. SPAD	.20	.70	.52	.29	−.281	.59	.470	.35	−.883	.12
Bg vs. SPAD	.74	.09	.73	.10	.089	.87	.388	.45	.900	.10
UN vs. Bg	.84	.03	.88	.02	−.254	.63	−.008	.99	.950	.05
UN vs. SPAD	.70	.12	.64	.17	.758	.08	.545	.26	.734	.27
UN vs. No. grains m^−2	.83	.04	.87	.02	−.444	.38	.225	.67	.744	.26
UN vs. developmental stage 24 June^a	−.06	.91	−.12	.83	.828	.04	.956	.003	.738	.26
NUE vs. developmental stage 24 June^a	.12	.83	.06	.91	.828	.04	.478	.34	.738	.26
EN,g vs. yellow flag leaf area^a	−.93	.008	.26	.61	−.783	.07	−.377	.46	.258	.74
CN,g vs. yellow flag leaf area^a	.83	.04	.62	.19	.638	.17	.261	.62	−.775	.23
NUE vs. yellow flag leaf area^a	.00	1	−.53	.28	.493	.32	.377	.46	.258	.74
EN,g vs. translocation	.77	.07	.88	.02	.975	.0009	.930	.007	.871	.13
CN,g vs. translocation	−.32	.54	−.09	.87	−.415	.41	−.317	.54	.648	.35
NUE vs. translocation	.87	.02	.11	.83	−.439	.38	.407	.42	−.835	.16
Translocation vs. yellow flag leaf area	−.46	.36	.35	.49	−.899	.01	−.319	.54	−.258	.74
NUE vs. straw biomass	.48	.34	.15	.77	.006	.99	.254	.63	.979	.02

Note: p-values < .05 in bold style.

^aSpearman correlation.

Figure 4. Relationship between (a) uptake efficiency (U_N) and growth stage (GS) on 24 June in spring wheat, LN (U_N= −43.19 + 1.30×GS, Spearman correlation coefficient = 0.83, p = .04), (b) U_N and GS in spring wheat, HN (U_N= −44.59 + 1.46×GS, Spearman correlation coefficient = 0.96, p = .003), (c) grain N concentration (C_N,g) and yellow flag leaf area (YFLA) in winter wheat, LN (C_N,g= 0.00699 + 0.00117×YFLA, Spearman correlation coefficient = 0.83, p = .04) and (d) grain-specific N efficiency (E_N,g) and YFLA in winter wheat, LN (E_N,g= 202.4–19.2×YFLA, Spearman correlation coefficient = −0.93, p = .008).

Notes: Symbols as in Figure 2. Data from the field experiment with spring and winter wheat varieties and two N treatments. Visual grading of flag leaf colour was carried out on 22 July (autumn varieties) and 28 July (spring varieties). The average percentage yellow flag leaf area was assessed according to the following scale: 1 = 0% yellow flag leaf area, 2 = 0.1–1.0%, 3 = 1.0–5.0%, 4 = 5–10%, 5 = 10–25%, 6 = 25–50%, 7 = 50–75%, 8 = 75–100%, 9 = dead. Statistics on correlations between variables are presented in Table 7.

Table A1. Means of NUE components and other traits recorded in the field experiment.

			NUE (g g^−1)		UN (g g^−1)		EN,g (g g^−1)		CN,g (g g^−1)		Ns (g m^−2)		Ng (g m^−2)		Bg (g m^−2)		N' (g m^−2)
Type	N treatment	Variety	Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE
Spring wheat	HN	Dala Landrace	10.7	0.6	10.7	1.1	47.2	4.3	0.0217	0.0005	0.611	0.021	6.50	0.29	299	9	6.51	0.62
	HN	Diskett	21.4	1.7	14.0	0.5	83.0	3.9	0.0183	0.0006	0.350	0.016	7.43	0.24	405	5	4.91	0.20
	HN	Granary	17.7	1.1	11.0	1.5	88.5	12.2	0.0190	0.0003	0.511	0.028	8.94	0.13	470	6	5.60	0.72
	HN	Quarna	20.8	1.9	16.1	2.6	62.5	6.9	0.0218	0.0006	0.378	0.025	7.74	0.27	355	9	5.90	0.67
	HN	Stilett	25.5	1.8	19.0	0.6	72.1	3.9	0.0186	0.0004	0.288	0.011	7.29	0.29	392	15	5.46	0.23
	HN	Vinjett	17.5	0.7	17.3	2.5	57.9	8.2	0.0186	0.0006	0.403	0.013	7.06	0.37	380	19	6.89	0.82
	LN	Dala Landrace	7.8	0.6	4.8	0.5	86.1	7.3	0.0190	0.0006	0.579	0.017	4.48	0.26	236	11	2.82	0.33
	LN	Diskett	15.1	1.4	9.7	0.8	90.8	5.7	0.0173	0.0006	0.336	0.013	5.05	0.34	290	12	3.22	0.19
	LN	Granary	10.2	0.8	4.8	0.8*	130.5	22.6*	0.0171	0.0005	0.526	0.009	5.37	0.38	313	17	2.52*	0.36
	LN	Quarna	13.3	1.0	10.7	2.6	67.4	9.4	0.0203	0.0007	0.366	0.003	4.87	0.33	241	21	3.91	0.92
	LN	Stilett	14.4	0.9	9.3	0.7	90.4	9.0	0.0174	0.0004	0.309	0.019	4.40	0.21	253	16	2.90	0.40
	LN	Vinjett	12.9	1.7	10.3	1.4	71.9	4.4	0.0176	0.0008	0.372	0.026	4.67	0.39	265	18	3.73	0.33
Winter wheat	HN	German Landrace	20.9	3.3	25.3	5.5*	47.2	5.5*	0.0188	0.0006	0.368	0.020	7.49	0.71	396	27	8.87*	1.49
	HN	Kranich	40.6	4.0	39.2	5.4	67.2	14.7	0.0168	0.0003	0.221	0.018	8.77	0.44	522	21	8.94	1.88
	HN	Harnesk	36.4	2.4	45.6	7.9	55.3	8.6	0.0157	0.0011	0.245	0.014	9.01	1.13	567	29	11.44	2.70
	HN	Kosack	45.9	5.9	52.7	6.1	52.9	4.6	0.0166	0.0005	0.203	0.014	9.13	0.80	548	32	10.47	0.60
	HN	Olivin	30.0	2.8	30.2	2.4	60.8	5.3	0.0164	0.0003	0.272	0.020	8.04	0.54	489	28	8.25	0.90
	HN	Loyal	32.8	2.1	44.4	10.4	58.7	13.0	0.0149	0.0004	0.253	0.004	8.33	0.56	557	26	11.16	2.51
	LN	German Landrace	10.7	1.5	15.8	1.0	41.2	3.9	0.0162	0.0001	0.404	0.029	4.17	0.28	257	15	6.34	0.46
	LN	Kranich	25.6	3.9	20.3	2.2*	66.8	5.5*	0.0165	0.0004	0.243	0.011	6.19	0.87	373	48	5.05*	0.77
	LN	Harnesk	23.1	3.0	21.2	4.0*	89.1	3.9*	0.0132	0.0002	0.233	0.010	5.31	0.48	402	35	4.74*	0.69
	LN	Kosack	21.4	2.2	16.9	3.4*	93.3	10.1*	0.0142	0.0005	0.222	0.010	4.69	0.32	331	22	3.55*	0.61
	LN	Olivin	23.7	3.7	24.2	4.2*	62.6	1.5*	0.0155	0.0003	0.264	0.007	6.21	0.94	399	53	6.40*	1.03
	LN	Loyal	19.4	0.8	17.7	1.3	82.1	6.3	0.0135	0.0002	0.252	0.013	4.86	0.22	360	19	4.50	0.54

Table

		Variety	SPAD value of flag leaf		Ears m^−2		Grains ear^−1		No. of grains m^−2		Plant height (cm)		Straw biomass (g m^−2)		Translocation		Yellow leaf	GS June 24
			Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE	Median	Median
Spring wheat	HN	Dala Landrace	36.3	0.5	466	16	24	2	11,870	297	120	2	616	28	0.58	0.07	4	38
	HN	Diskett	40.8	0.2	460	24	27	2	12,969	144	85	1	615	58	0.88	0.07	4	41
	HN	Granary	39.6	0.9	454	14	31	1	15,158	391	88	1	600	53	1.03	0.22	3	38
	HN	Quarna	42.5	0.4	519	25	23	2	12,527	521	87	2	571	45	0.80	0.14	7	41
	HN	Stilett	40.3	0.6	488	22	30	2	15,437	604	75	1	644	82	0.76	0.05	5.5	43
	HN	Vinjett	39.3	0.7	488	15	25	1	12,694	640	91	1	565	66	0.60	0.07	5	43
	LN	Dala Landrace	29.1	1.0	411	18	21	0	9195	403	98	4	480	74	0.91	0.08	4	37
	LN	Diskett	34.6	0.1	391	10	23	1	9577	351	73	4	488	49	0.88	0.09	5	41
	LN	Granary	32.1	0.5	441	7	22	2	10,500	596	70	4	363	62	1.23*	0.22	3	37
	LN	Quarna	36.1	0.5	483	7	17	1	8869	874	72	4	457	85	0.76	0.11	6	41
	LN	Stilett	33.2	0.8	419	25	23	2	10,336	889	66	1	387	31	0.86	0.10	5.5	41
	LN	Vinjett	32.1	0.7	427	18	20	2	8840	584	76	5	409	59	0.70	0.07	5.5	41
Winter wheat	HN	German Landrace	39.4	1.5	280	21	34	2	9919	666	128	6	809	48	0.58	0.04	7	55
	HN	Kranich	43.6	0.9	385	12	36	1	14,846	681	75	4	769	60	0.83	0.17	7	59
	HN	Harnesk	43.6	2.2	425	19	38	1	17,125	1250	71	2	660	122	0.57	0.06	5	56
	HN	Kosack	41.6	0.7	363	10	44	4	16,590	1179	103	6	908	122	0.59	0.06	4.5	53
	HN	Olivin	39.8	0.6	406	34	34	2	14,434	737	87	6	841	110	0.78	0.11	6	54
	HN	Loyal	41.5	1.4	414	20	36	2	15,818	946	75	3	722	100	0.65	0.15	5	56
	LN	German Landrace	30.3	0.6	283	15	22	2	6532	443	112	6	499	92	0.40	0.05	8.5	56
	LN	Kranich	38.3	1.3	353	20	28	2	10,524	1385	72	7	572	63	0.80*	0.11	7	59
	LN	Harnesk	33.9	1.3	349	18	31	4	11,366	895	67	7	592	59	0.69	0.09	6	55
	LN	Kosack	33.5	0.6	366	14	26	2	10,080	671	92	8	704	93	0.83	0.14	6	52
	LN	Olivin	36.2	2.0	359	9	31	3	11,865	1336	83	11	564	61	0.70*	0.10	7	55
	LN	Loyal	33.5	0.7	335	19	28	1	9795	430	69	8	575	85	0.72	0.04	6	57

Notes: GS=growth stage according to Tottman (1987), abbreviations of NUE components according to Table 1. Mean values and standard errors of the mean are presented.

*Three replicates instead of four.

Table A2. Mean aboveground biomass of winter wheat seedlings sampled in the winter and in the spring.

Variety	Aboveground biomass in winter (g plant^−1)		Aboveground biomass in spring (g plant^−1)
	Mean	SE	Mean	SE
German Landrace	0.0233	0.0011	0.0643	0.0075
Kranich	0.0157	0.0002	0.0462	0.0015
Harnesk	0.0166	0.0007	0.0444	0.0002
Kosack	0.0171	0.0005	0.0483	0.0025
Olivin	0.0133	0.0004	0.0405	0.0033
Loyal	0.0153	0.0010	0.0458	0.0019

Note: Mean values and standard errors of the mean are presented.

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